Observability of Josephson pair-quasiparticle interference in superconducting interferometers

Abstract

Pair-quasiparticle interference current has a measurable effect on the tuning characteristics of a superconducting interferometer operating in the nonhysteretic regime: $\ensuremath{\epsilon}\ensuremath{\equiv}(\frac{2\ensuremath{\pi}}{{\ensuremath{\Phi}}_{0}}){L}_{R}{I}_{c}<1$ where ${\ensuremath{\Phi}}_{0}=\frac{h}{2e}$, ${L}_{R}$ is the inductance of the interferometer ring, and ${I}_{c}$ is the critical current of the interferometer's weak link. In the limit $\ensuremath{\epsilon}\ensuremath{\ll}1$ the interferometer will have a zero crossing in its magnetic flux sensitivity versus frequency characteristic that is above, on, or below resonance depending whether the coefficient of the interference current term is positive, zero, or negative, respectively. For larger $\ensuremath{\epsilon}$, screening currents will also shift the zero crossing. Results for the magnitude of this additional shift are presented and discussed.